In the packaging of pulp products, especially stacks of facial tissues and paper handkerchiefs, a considerable problem arises because the articles to be packaged are compressed to a considerable extent. It is therefore difficult to produce an exact cuboid pack.
To this end the drum machines for wrapping packs of facial tissues and paper napkins generally use an apparatus called a “revolver.” The revolver is essentially a drum that rotates about a horizontal axis. The revolver is typically provided with a plurality of radially disposed chambers, often called “revolver pockets.” These revolver pockets generally provide the forming geometry for the articles to be packaged. Within the revolver pockets, the packs of facial tissues and paper handkerchiefs to be wrapped are individually inserted in rapid succession. Each pack to be wrapped is fed by a driving chain and compressed prior to the introduction into a corresponding revolver pocket.
The insertion takes place with the simultaneous interposition of a film of suitable plastic material provided for wrapping the facial tissues and/or paper handkerchiefs (i.e., to make up the envelope) after having been properly folded around the sides of the pack and closed by welding and/or gluing. Owing to the high rotary speed of the revolver, it is usually necessary to feed and compress the facial tissues and/or paper handkerchiefs at a rate sufficiently high to allow for successively engaging all the revolver pockets to ensure a convenient productive capacity of the plant. This implies a synchronization with minimum tolerance margins of the steps for feeding, squeezing and, then, inserting the facial tissues and/or paper handkerchiefs into the revolver pockets, mainly as a function of the revolver peripheral speed and of the variation of the momentum to be imparted to each pack prior to the insertion thereof into the revolver pockets.
Thus, the adoption of suitable criteria in the management of the plant, in relation to both the choice of the most suitable operating speeds and the maintenance and adjustment of the individual devices, is required to allow provide complete operative integration and maximum reliability. It is well known, the level and rate of activities for the maintenance and adjustment of the components weigh heavily on the economic efficiency of the plant and, accordingly, on the cost of fabrication of the finished packaged product. Thus, there is a strong demand to use simpler and more robust equipment and processes to improve the reliability of the production systems and reduce the relevant costs related to the manufacture of the packaged product.
Some prior art equipment requires a stoppage for each group of napkins before operating the squeezing and the subsequent insertion thereof into the revolver pockets, and for bringing the compressive means back to the respective initial operating condition before starting the wrapping of a new group of napkins. That is, bringing the compressive means back behind the next group of napkins to be wrapped, so that the feeding thereof to the revolver results discontinuous. Moreover, the functional construction of known apparatus does not allow an increase in the output of the plant, that is, in the napkins-feeding rate, beyond a given value corresponding to the operating speed of the compressive means. In addition to this, there is the fact that the constructional complexity of this known apparatus brings about an intense servicing activity which weighs on the production cost of the packaged product. Such equipment is described in U.S. Pat. No. 4,845,924.
Another packaging machine can utilize a pair of belt conveyers converging towards an articles-compressing device which is made up of a pair of parallel horizontal superimposed belts for moving the napkins delivered from the feeding belts, and also made of a vertical operating cylinder, in a fixed position, provided with a flat head and a corresponding stationary abutment surface, to compress the thus fed napkins. However, this known apparatus also provides for a discontinuous feeding of napkins, owing to the stoppage of the belts of the compressive device, which is necessary to allow for the intervention of the compressive cylinder. Accordingly, the output capacity of the plant cannot be raised beyond a value corresponding to the operating speed of the cylinder. Such equipment is described in German Patent DE 2322878.
Other machines or processes related to high speed packaging can use a drum provided with radial pockets with dimensions that are suitable for the product to be packaged, inside which the stacks of product to be packaged are inserted in rapid succession, with the simultaneous interposition of one blank plastic film, so as to obtain the complete wrapping of each stack, completed by welding applied on the film to obtain a closed packaging. This arrangement of equipment of this type is described in U.S. Pat. Nos. 4,845,924 and 5,459,979.
In machines of this kind, due to the high operation speed that is required to ensure suitable productivity, it is very complex to compress the stack, keep its correct geometry and carry out the insertion inside the pockets of the drum without causing deformations or faults in the wrapping by the film. In particular, but not exclusively, it is difficult, if not impossible, to keep control of the position of the film and of the compression in the radial direction of insertion during the wrapping step when the speed increases beyond a certain limit, causing defects in the package which, in any case, can occur also when the speed is kept below said limit. Thus, it would be beneficial to provide an apparatus for packaging stacks of facial tissues and/or paper handkerchiefs that provides better throughput, increased reliability, and a packaged product with a better finished appearance to increase consumer appeal.